It has been found difficult to machine internal or external threads into a workpiece without requiring a lead-in or exiting thread. As typical in the art, thread cutting of a workpiece is accomplished by a turning operation, in which the feeding per revolution of a cutting insert ordinarily corresponds to a thread pitch. The pointed end of the insert is usually cut to a profile intended to correspond to, for example, the space between the threads. The turning operation of feeding the insert through the workpiece produces lead-in and exiting threads. These lead-in an exiting threads are characteristically less in thickness and height than the threads used for securing the workpiece. Ordinarily, the workpiece is then heat treated to provide threads suitable for the amount of tightening force that is required to keep the threaded joint securely fastened. It is critically important to have all the threads heat treated to provide stability to the threaded joint. One potential source of damage occurs when the corresponding workpiece to be secured is over tightened when screwed together. This could cause the lead-in and exiting thread to chip or completely brake away from the workpiece. An application where this may be damaging is, for example, a fuel injector where the lead-in and exiting threads chip off and work their way through the injector down to a nozzle tip thereby blocking a fuel injection orifice. The blocked fuel injection orifice leads to improper injection of fuel thereby providing a less efficient combustion process in an internal combustion engine.
The present invention is directed to overcoming one or more of the problems as set forth above.